Among conventional route search devices capable of searching for a route with the lowest carbon dioxide emission, there is a route search device in which a carbon dioxide emission that varies in accordance with a distance of each section (hereinafter, referred to as a link) is identified by calculating a coefficient in accordance with a road gradient state of the section based on a difference in height between both ends of the section stored in a storage medium and then multiplying a distance of each section by the coefficient, and additionally a carbon dioxide emission that varies in accordance with a traveling time of each section and a carbon dioxide emission based on an index that varies in accordance with the number of stops in each section are separately identified, and moreover the respective carbon dioxide emissions thus identified are summed so that a carbon dioxide emission of each section is calculated (Patent Document 1).
In the route search device of the Patent Document 1, a difference in height of each link is obtained by using a difference in height between a start point and an end point of the link (see paragraph [0052]), and a gradient of the link is expressed by using a relationship of “sin°=the difference in height (between both ends of the link)/distance (of the link)” (θ: the angle formed between a horizontal plane and the link) (see paragraph [0048]). Thereby, a fuel consumption concerning position energy caused by the difference in height between both ends of the link is obtained. Although the gradient θ is explained in the description of paragraph [0048], the fuel consumption is eventually calculated based on position energy (mg×the difference in height (between both ends of the link)) caused by the difference in height between both ends of the link. Therefore, an influence of the degree of the gradient, such as a gentle upslope or a steep upslope, is not considered. Accordingly, this technique presupposes a link in which the gradient is constant (the gradient does not vary depending on a location in the link) and a fuel consumption concerning position energy of the link.
On the other hand, in a route search device of a car navigation system or the like, such a technique is disclosed that not only a low-level road network having a large amount of information (having detailed information) but also a high-level road network having a small amount of information (abstracted) is held in map data so that an increase in a calculation time required for a route search and in a memory capacity is suppressed even in a case where a distance from a departure place to a destination place is long (for example see Patent Document 2).